1. Field of the Invention
This invention generally relates to a molding method for a semiconductor chip package and more particularly to a molding method for a BGA semiconductor chip package.
2. Description of the Related Art
FIG. 1 illustrates a molding device for a conventional BGA (ball grid array) semiconductor chip package. The molding device comprises a plurality of pots 2. Two substrates 20 are placed at two sides of the pot 2 for supporting an array of chips 12. The runner 3 independently extends from one side of the pot 2 to the comer of the substrate 20, and connects to the upper part of a mold disposed on the substrate 20 through a gate 4. Under the pressure created by the plunger 15, the molding compound 14 is forced out of the pot 2 and then passes through the runner 3 and the gate 4 to enter the cavity of the upper part of the mold. When the molding compound 14 fills the cavity, the plunger 15 stands still for a predetermined time until the molding compound 14 cures. Then the plunger 15 is raised, the top part of the mold is opened, and the molded product is removed from the mold. Extra parts such as runners and gates are removed from the molded product, and then the molded product is sawed into individual units, whereby the BGA semiconductor chip packages are completed.
According to the molding device for a conventional BGA semiconductor chip package described above, since the molding compound 14 is transferred into the cavity of the upper part of the mold through the gate 4 on the comer of the substrate 20, the pressure of the molding compound distributed unevenly inside the cavity during encapsulation thereby creating the problem of wire sweeping and molding defects such as voids or holes. Further, since the flow path of the molding compound within the cavity is longer, the period of the molding cycle is prolonged and variations of the property of the molding compound between different positions due to heating are enlarged thereby influencing the molding quality.
It is a primary object of the present invention to provide a molding method for a BGA semiconductor chip package wherein the problem of wire sweeping is improved thereby increasing the yield of product.
It is another object of the present invention to provide a molding method for a BGA semiconductor chip package which is effected by a molding die having a cavity connected to a plurality of runners interconnected by a molding pressure balancing device allowing effective controlling of the molding compound such that the flowing and filling thereof are more even thereby reducing the period of encapsulation, and thereby improving the molding quality.
A molding method in accordance with the present invention is used to encapsulate an array of chips having two lines of bonding pads formed at two respective side thereof. Each chip is electrically interconnected to a substrate through a plurality of bonding wires. The molding method comprises: (A) providing a molding apparatus comprising a molding die having a molding cavity and at least two runners connected to the molding cavity; (B) closing and clamping the molding die in a manner that the chips are located in the molding cavity thereof; (C) transferring a molding compound into the molding cavity wherein each chip is arranged in a manner that the two lines of bonding pads thereof are substantially perpendicular to flowing direction of the molding compound; (D) curing the molding compound; and (E) unclamping and opening the molding die to take out the molded product. According to the molding method of the present invention, the two lines of bonding pads of each chip are substantially perpendicular to the flowing direction of the molding compound, hence the bonding wires are substantially parallel to the flowing direction of the molding compound such that the influence of the molding compound is suppressed thereby reducing the occurrence possibility of wire sweeping and increasing the yield of product.
The molding apparatus in accordance with the present invention preferably includes a molding pressure balancing device for providing interconnection between the runners thereby balancing the pressure of molding compound inside each runner whereby the molding compound can be transferred into the molding cavity more evenly.